As a method for measuring a mass of particulate matters (PM: in this specification hereinafter also called as PM) as being one of emission matters from an engine known is a filter mass method. The filter mass method is a method for collecting the PM by arranging a collection filter on a flow channel of an exhaust gas from an engine and measuring a mass of the collected PM by the use of a balance or the like. Since the filter mass method can directly measure a mass of the PM in which practically exists no reference material whose physicality can be specified, it is possible to expect certainly and correctness of the measurement. As a result, among measurement devices using the filter mass method used for an exhaust gas test presently on a standard basis is a constant volume sampler (CVS) that dilutes all amount of the exhaust gas from an engine and conducts an analysis.
Meanwhile, with the view of further improving engine performance or an environmental problem there is recently a request that a time series change of the PM emission amount while the engine is dynamically in operation on a road or the like be measured. However, since the filter mass method is, so called, a batch-type measurement method wherein only an integrated mass of the PM discharged during a certain period can be measured, it is not possible to know how the mass of the PM changes from moment to moment in accordance with a dynamic driving situation.
Then as an alternative method for the filter mass method proposed or developed are an FID (Flame Ionization Detector), an ELPI (Electric Low Pressure Impactor), an SMPS (Scanning Mobility Particle Sizer), a DCS (Diffusion Charger Sensor) (Patent document 1). The FID is to measure a number of carbon atoms in a sample gas, and the ELPI and SMPS are to count a number of particles. In addition, the DCS is to charge a surface of the particles and to measure a charged amount.
In accordance with these devices, although it is possible to conduct a measurement during a road travel, however, the measurement is to measure the number of carbon atoms, the number of the PM, or the surface area of the particles, and is not to measure the mass of the PM directly. As a result, in order to obtain the mass of the PM from these measurement results, it is necessary to obtain a correlation between the measurement result and a measurement result by the collection filter measurement method conducted under the same condition, and to calculate the mass of the PM based on the correlation.
Then, it can be conceived that a correlation between a measurement result by the filter mass method and a measurement result by the ELPI method in each driving state of the engine is previously obtained, and a dynamic change of the mass of the PM is calculated by applying this correlation to the measurement result by the ELPI during the road travel.
However, since this correlation is consistently a correlation at a time when each driving state of the engine is kept in a constant static state, it is a little unreasonable that this correlation is directly applied to a case of the road travel such that the dynamic driving is conducted and that the result is estimated as the actual dynamic change of the mass of the PM.